Metal cupping process



Feb. 18, 1947. R. E CKSTEIN 2,415,940v

' METAL CUPPING PROCESS Filed 005. 5, 1944 I INVENTOR. GEORGERLECKS-TE/N.

AGENT Patented Feb. .18, 1947 UNITED s ArEs fPAT'ENr orrice M TALcurrm'c rnocnss George R. Eckstein, Bridgeport, Conn., assignor toRemington Arms Company, Inc., Bridgeport, Conn., a corporation ofDelaware f Application October 5, 1944, Serial No. 557,351

The present invention relates, in. general, to

metal drawing, and, in particular, to an improved means and method offorming cups from steel blanks for the manufacture of small arms ammu-.nition components, as, for example,.caliber .50 steel cartridge cases,

Cartridge cases have been manufactured from time immemorial by punchinga metal blank from a sheet of brass, cupping the blank and subsequentlysubjecting-the cup to a number of deep drawing, annealing and trimmingoperations to secure the properi shape and dimensions of the case. Brasshas been used almost exclusively in the manufacture of cartridge casesbecause its j metallurgical characteristics are such as to tender abrass blank amenable to the deformations and stresses which areintroduced into the metal during the shaping of the case, and to whichthe -finished case is subjected when fired.

The problem of manufacturing steel cartridge cases in quantityproduction lots has not been solved heretofore due primarily to the highmodulus of elasticity of steel, its low rate of .work, hardening and itshigh corrodibility. Other factors such as the heterogeneous nature ofsteel,

the relative difficulty with which it can be worked and the tendency ofworkpieces to pick up or cling to the draw punches have also contributedto the problem of manufacturing steel cartridge cases on a commerciallysuccessful basis.

In view of these factors, it is not surprising to find that a steelblank reacts differently than 3 Claims. (em-148a when such cases arefired have their origin in the cup for whereas malformed brass cups areamenable to correction during subsequent drawing operations anyeccentricity, asymmetry or other defects of a steel cup will not becorrected as the cup is being processed. Hence it is of paramountimportance that a steel cup have the highest degree of perfectioninorder to insure satisfactory cases.

Extensive experimentation has demonstrated that of the requisitecharacteristics of a steel cup for making .50 caliber'steel cases, itssusceptibility to processing by drawing; exterior walls free fromshearsurface; and a lip comprising substantially the entire shearsurface of the blank and having a prescribed contour, are among the mostimportant.

An object of 'the present invention is, therefore, the provision of ameans and method of forming cups of steel which can be processedsuccessfully to form drawn steel articles. A further object is theprovision of steel cups which will yield steel small arms ammunitioncomponents equivalent to brass in substantially all respects andin'quantity production lots, A still furtherobjectis the provision of ameans and method of blanking sheet steel and drawing the resulting blankto form steel cups wherein the shear surface-of the blank is confinedsubstantially Wholly to the lip of the cup. Astill further.v object isto provide a method of drawing steel cups embodying the step of coiningthe lip of the cup,

These and other objects, features and advantages of the invention willbe more fully described in the following specification and illustratedin the accompanying drawing, in which:

Fig.1 is a representation of a macrophotograph of asectioned wide anglesteel blank showing the one hundred and fifty times that heretofore'encounteredin the manufacture of deep drawn steel articles. As might beexpected, therefore, theusual means and method of drawing steel blanksare not applicable to the manufacture of steel cartridge cases.

Moreover, it has been discovered, as a part of this invention, that alarge proportion of the defects which have been found in finished steelcarverted blank, but before the lip of the cup has flow lines of themetal at the tshear surface and includes a fragmentary'view of ablanking punch and die assembly.

Fig. '2 is a representation of a macrophotograph of a sectioned steelcup formed from an inverted blank showing the formation of the fractureline in the outer wall of the cup.

g. 3 is a representation of a macroph tograph of a sectioned steel cupformed from a noninbeen coined. v

Fig. 4 is a fragmentary side elevation in section of the improvedcupping punch and die assembly of this invention.

Fig.5 is a representation of a macrophotograph tridge cases asheretofore made or which occur of a sectioned steel cup having a planarbevelled ing punch and die assembly comprises a cylindrical member ID,the diameter of which is substantially 1.443 inches and 0.110 inch lessthan the diameter of the blanking die aperture ll. Due to the differencein diameter of the blanking punch and blanking die aperture, the angleof the shear surface l2 of the blanked disc B is relatively wide beingof the order of 15 which is conducive of a clean cut shear surface.Moreover, the shear surface of the blank hereinafter termed a wide angleblank is necked down or pinched during the blanking operation, as shownby the flow lines in Fig. 1, .so that the area of the shear surface isreduced. This effect minimizes the tendency of the shear surface towrinkle during the subsequent cupping operation, which tendency has beenfound to induce incipient cavities in the lip of the cup and topropagate cold shuts during subsequent drawing operations. Although ablanking punch'die clearance of 0.110 inch is preferred, satisfactorywide angle blanks have been formed with a blanking punch and dieclearance as small as 0.083 inch.

Heretofore, efforts were made to cup steel blanks in the so calledinverted position, that is to say, the blank was turned over beforecupping so that its top or surface of small diameter seated inthecupping die, a noninverted cup being one whose blank has been seatedbottom down in the cupping die.

Fig. 2 shows an inverted cup or cup formed from an inverted blank. Ithas been found as a part of this invention that inverted steel cupsinvariably develop a. fracture line in the outer wall which carriesthrough into the completed cartridge case which may result in casebreakoifs during final drawing, ruptures on firing and localizednecking. Moreover, this fracture line was found to coincide invariablywith the bottom edge II! of the shear surface l2 of the blank which, asshown by the metal flow lines in Fig. 2, doesnot form the lip of the cupas might be expected but, due to a nonuniform flow of metal at the topand bottom of the inverted blank, is drawn down over into the outsidewall of the cup.

The present invention relates in part to a method and means ofeliminating the fracture line in steel cups based upon the concept thatby confining the shear surface of the blank to the lip of the cup, theshear surface and fracture line, if such should occur, may be completelyeliminated from the drawn case at least by the second cut-off andwithout a prohibitive waste of material. a

It was discovered that an important factor contributing to theconfinement of the shear surface of a wide angle blank to the lip of acup was the concept of seating the blank bottom down or in a noninvertedposition in the cupping die.

Fig. 3 illustrates a cup formed from a noninverted blank. It will benoted that the shear surface i2 of the noninverted blank has been heldsubstantially to the lip of the cup and that the nature of the flowlines of the metal is such that the bottom edge 13 of the shear surfacehas not been turned outwardly into the outer wall of the cup as occursin the inverted cup shown in Fig. 2. This characteristic metal flow ofthe noninverted blank is due in part to the fact that the larger by thecoining amount of metal in the bottom of the blank en- .ables the metalto stretch sufliciently before becoming work hardened to permit thelower edge l3 of the shear surface of the blank to gain the lip of thecup. It will be noted that the flow lines of the metal of a noninvertedcup run out completely into the lip and that these flow lines aresubstantially parallel to the inside and outside walls of the cup.

Other factors, however, are influential in shaping the lip of the cup.It will be noted that the lip i2 of the cup shown in Fig. 3 is somewhatconcave and during subsequent drawing operations this condition tends tobe aggravated resulting in the formation of cold shuts in the mouth of adrawn case. The concave contour of the lip may be due in part to thateffect known in the art as pull up, wherein the outside edge of the lipof the cup is pulled up higher than the inside edge. As a part of thisinvention, it has been found that the amount of pull up increases withan increase in size of the ledge or shelf of the cupping die hereinafterdescribed, and, on the other hand, a shelf of appreciable size isessential to the stability of the blank which in turn is an importantfactor in securing wall concentricity. Accordingly, a cupping die wasdeveloped as shown at M in Fig. 4 which embodies a minimum ledge orshelf l5 comprising a compound curve, the upper portion of which has aradius R1 of substantially 0.100 inch adapted to blend into the lowerportion of the curve, the radius R: of which is substantially 0.234inch.

Referring to Fig. 4, the diameter of the bottom of the blank is shown assubstantially equal to the diameter of the cylindrical mouth ll of thecupping die I4 which in the embodiment shown is substantially 1.555inches diameter and inch deep. The portion of the cupping die aperturebetween the lower end of the shelf [5 and the upper edge of the die landshown at I8 is known as the approach surface and comprises a conicalsurface [9 which makes an angle of substantially 12 with thelongitudinal axis of the die. The lower end of the approach surface 19is blended into the land 10 by a radius R3 of substantially 1; of aninch. The diameter of the land is substantially 1.177 inches, its depthbeing substantially 0.090 inch. As is the usual practice, the lower edge20 of the land is square and sharp to facilitate stripping, acounterbore 22 being provided on the underside of the cupping die id tomaintain the sharp edge 20 of the land. It will be understood, however,that an independent stripper die may be used.

The particular cupping die contour defined by the shelf [5, the conicalapproach surface I9 and the radius R: which blends the latter into theland i8 has the effect of forming a cup lip which is substantially freefrom pull up, fringe and cavities, the shelf IS, in particular, insuringsufficient blank stability to guarantee cups having concentric walls andbottoms symmetrical with respect to the walls.

bility. The punch may be guided in its reciprocable movement withrespect to the die 14 by means of a guide sleeve 24 which, in the usualpractice, is resiliently mounted and adapted to enter the mouth I! ofthe cupping die slightly in advance of the cupping punch. The means foractuating the cupping punch 23 and its guide of substantially 56 withrespect to 24 are conventional and well known in the art I and hence hasnot been shown. The lower end of the punch is reduced to provide aslightly tapered nose 25 which is substantially 0.837 inch in diameterat its lower end and 0.400 inch long.

In the present embodiment, the radius R4 of the end of the nose issubstantially of an inch.

The upper end of the nose 25 is substantially 0.847 inch in diameterandis joined'to the lower end of the shank 23 by an integral conicalshoulder 26, the slope of its surface making an angle tudinal axis ofthe punch. I

The conical shoulder 26 of the cupping punch I invariably produces adefective piece for drawing.

As pointed out above, anoninverted blank cupped in'a die having thecontour specified above has its shear surface held to the lip of thecup, the walls of the cup being concentric and the base of the cupsubstantially symmetrical with respect to the walls. Moreover, .the lipof the cup is free from such defects at pull up, fringe and cavities.

It has been found, however, that the lip does not invariably have theprescribed contour for insuring optimum results in subsequent drawingoperations.

Generally, the lip will comprise a surface sloping from the outer edgeof the cup inwardly and downwardly, the profile of the surface beingslightly concave adjacent the inner edge of the cup, as shown atl inFig.6. As a part of the present invention, it was conceived that byproviding a suitable shoulder on the cupping punch, the concave portionof the lip could be ironed out so as to make true the'optimum lipprofile. To this end, the intersection of the conical shoulder 26 of thecupping punch with itssllght- 1y tapered nose portion comprises arelatively sharp corner; 21.

Referring to Fig. 6, it will be seen that when this sharp corner strikesthe inner edge of the lip of the cup, the metal atthis section ofthe lipwill be, flattened and simultaneously displaced outwardly toward theouter edge of the cup by the coining action of the bevelled shoulder26.. In this manner, the concave portion I20 of the surface of the lipis eliminated and a substantially planar bevelled surface on the lipwillbe made true. I

The sharpness of the corner 21 and the location, on the punch of theshoulder 26,- which is hereinafter termed a coining shoulder, has beenarrived at byextensive experimentation and constitute features which areessential to the formation ofthe optimum profile. It has also beenascertained that the coining shoulder resists a tendency of the shearsurface of the lip of the cup to move down-into the inside wall thereofand that by maintaining a coining shoulder of substantially thedimensions and configuration described, blank thicknesses varying as'much as 0.010 inch may be cupped successfully 75 the longielled surfacethereon.

and considerable latitude may be enjoyed 'in the cupping die profile.Fig. 5 shows the effectiveness with which the coining shoulder 26 andthe sharp corner 21 of the cupping punch have held the shear-surface l2of the cupped blank from moving down intothe wall of the cup whilesimultaneously coining a substantially flat bevel 111130 on the cup Itwill be understood that the resistance sufficient to effect a swaging orcoining action is provided by the radial pressure acting between thewalls of the cup and the walls of the die aperture during the drawingoperation.-

During subsequent draws, the .lip of the cup mouth of the case free fromshear surface metal or fracture line defects.

The method of blanking and cupping is believed to be clear butmay bebriefly described as follows: A strip of steel Mis fed across theaperturell of the blanking die whereupon the blanking punch I0 is drivendown onto themetal strip. The blanking punch, blanks out'a disk B havinga sharp clean shear surface l2 which makes an and hence the shearsurface tend to pull down inangle of substantially 15 with respect tothe top and bottom surfaces of the blank and which is slightly necked asdescribed above. The blank B is removed from the blanking die and may becleaned and covered with a suitable lubricant or thin copper plating.The blank is then seated bottom down, that is to say, in a noninvertedposition on the shelf I5 of the cupping die It. When the cupping punch23 is driven down onto the topof the blank, the latter, will be forceddown'through theconical approach surface l9 of the cupping dieand intothe cylindrical land Hi. During this interval, the coining shoulder orlip 26 of the cupping punch coins the shear surface |2 of the cuppedblank, as indicated in Fig. 6, so as to iron out its profile and maketrue a planar inwardly and downwardly inclined bev- On completion of thedownward stroke of the cupping punch, the

punch is withdrawn from the cupping die. The

cup having expanded radially slightlyafter passing through the land 3now engages the sharp 60 edge 20 of the land which strips the cup fromthe'cupping punch in theusual manner.

The method and means described for forming a steel cup contemplates theuse of separate machines for blanking the disk and cupping the blankeddisk and'in view of the relatively high such as used extensively inblankingand cupping brass may be used for forming steel cups.

It will be understood that the dimensions, proportions, angles and radiigiven in the foregoing description are those which have been found.optimum for making a steel cup to be further processed into a caliber.50 cartridge case and are illustrations of and not limitations upon theinvention.

What is' claimed is:

piece having concentric walls which are free from shear surfacecomprising the steps of punching a frusto-conical blank from a sheet,insertingsaid 1. A method of making a-cup-shaped draw the mid-portionthereof into a reduced diameter portion of said die, and then forcingthe cup through and out of the reduced diameter portion of the die whileapplying to the lip thereof a pressure which induces an outward radialflow of the metal adjacent said lip.

2. A method of making a cup-shaped draw piece having concentric wallswhich are free from shear surface comprising the steps of punching afrusto-conical blank from a sheet, insertingsaid frusto-conical blankwide base foremost in a draw die, cupping said blank by engaging andforcin the mid-portion thereof into a reduced diameter portion of saiddie, forcing all of the shear surface of said blank into the lip of thedrawn cup, and then forcing the cup through and out of the reduceddiameter portion of the die while applying to the lip thereof a pressurewhich induces an outward radial flow of the metal adjacent said lip.

3. A method of forming a cup-shaped draw piece having concentric wallswhich are free from shear surface comprising the steps of providing aflat circular blank having a sheared edge portion of frusto-conicalconformation, supporting said blank in a cupping die with itsfrusto-conical sheared edge flaring outwardly in a direction facing thedie land, cupping said blank by engaging and forcing same through saidcupping die with a cupping punch, and simultaneously shaping the shearededge to define an inwardlybeveled lip by engagement with said shearededge with an inverted frusto-conical shoulder formed on said punch.

GEORGE R. ECKSTEIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

